Thermoplastics are a type of polymer compounds that can be formed using heat and/or pressure. They are easy to process, melt when heated, and return to a solid state when the temperature is sufficiently lowered.
Thermoplastics are easy to process in various forms, and some of them can be recycled. Therefore, in modern society, various kinds of plastic molded products are used.
These plastics are generally obtained by polymerizing monomer compounds. The polymerized resin or resin composition is processed into pellets and stored, followed by molding using various methods depending on each application to produce products.
Among these, the polyethylene resin is widely used in various fields such as those utilizing films, sheets, and pipes, since it has excellent mechanical properties such as stiffness, impact resistance, environmental stress crack resistance (ESCR), and elongation characteristics, and is also excellent in chemical resistance, corrosion resistance, and electrical properties.
Particularly, when the polyethylene resin is used for a hollow molded article, a coated product, a pipe, or the like, physical properties such as corrosion resistance and long-term durability are considered to be important. In particular, in case of a pipe or the like, long-term durability of at least 20 years, generally 50 years or more, is required.
For a thinly processed polyethylene resin product, it is common to increase density of the polyethylene resin in order to maintain the strength required for the product. Since the polyethylene resin having high density tends to have low long-term durability, it is not easy to maintain long-term durability at a certain level while maintaining the strength of the product.
Because of these characteristics, the properties related to the long-term durability of the polyethylene resin should be accurately measured and evaluated. In general, in order to measure the long-term durability of the polyethylene resin by a conventional method, a long time, usually 500 hours or more, or 1000 hours or more, is required, which is a main factor for delaying product development.